Device for detecting stop value data from flash unit used with camera

ABSTRACT

In a flash unit used with camera for providing stop value data consisting of a frequency clock, a circuit which can detect stop value data consisting of a frequency clock or the like provided from the flash unit without being influenced by noise by permitting the stop value data to be accepted when the data is confirmed to be a continuous normal signal. Where the camera is provided with a TTL flash automatic light does control unit, the circuit permits the use of a common circuit for a path through which the detecting circuit receives the stop value data and for a path through which the TTL flash automatic light dose control unit provides automatic light dose control data to be flash unit, thus permitting simplification of these data transmitting system.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a stop value data detecting device for a camera which can be used with a flash unit connected to it for providing stop value data consisting of a frequency clock and with an automatic stop control unit.

2. Description of the Prior Art

Japanese patent application No. 56-88,532 filed by the same applicant as of the instant application discloses the use of a pulse signal consisting of a frequency clock as stop value data generated from a flash unit. However, no circuit which can detect the stop value data noted above has yet been proposed.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a circuit, which can detect stop value data consisting of a frequency clock or the like provided from the flash unit without being influenced by noise by permitting the stop value data to be accepted when the data is confirmed to be a continuous normal signal. Another object of the present invention is to provide a circuit for use in case where a TTL flash automatic light dose control unit is provided, which permits the use of a common circuit for a path through which the detecting circuit receives the stop value data and for a path through which the TTL flash automatic light dose control unit provides automatic light dose control data to the flash unit, thus permitting simplification of these data transmitting systems.

According to the present invention, the clock is supplied to an automatic stop control unit after a stop value detecting circuit confirms that the frequency clock which is provided as the stop value data from the flash unit consists of pulses greater in number than a predetermined number, whereby the possibility of transmission of such noise as one consisting of an insufficient number of pulses with respect to the aforementioned number to the automatic stop control unit is prevented. Further, in case of a camera provided with a TTL flash automatic light dose control circuit, an input/output selecting circuit transmits the stop value data from a flash unit to the stop value detecting circuit when there is no shutter release signal and also there is no light dose control signal from the TTL flash automatic light dose control circuit while when there is a shutter release signal and also a light dose control signal is produced from the TTL flash automatic light dose control circuit, it transmits the light dose control signal to the flash unit. Thus, it is possible to make common use of the input/output path of the flash unit and simplify the data transmitting system.

The above-mentioned and other objects and features of the invention will become apparent from the following detailed description taken in conjunction with the drawings which indicate an embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an embodiment of the present invention;

FIG. 2 is a circuit diagram showing a specific example of the construction of the flash unit and input/output selecting circuit;

FIG. 3 is a specific example of a stop value detecting circuit; and

FIG. 4 is a timing chart for explaining the operation of the stop value detecting circuit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows the construction of the embodiment. A flash unit 1 is connected to an input/output selecting circuit 2 through a zero potential terminal GND and also through a signal potential terminal Q₀. The flash unit 1 can provide stop value data consisting of a frequency clock and is also capable of light dose control by a TTL automatic light dose control unit. The input/output selecting circuit 2 receives a signal P₁, which is provided from an exposure calculating circuit 3 constituting an automatic stop control and is capable of assuming a high (H) level or a low (L) level, and a signal P₂, which is provided from a TTL flash automatic light dose control circuit 4 and is capable of assuming a high (H) level or a low (L) level. The input/output selecting circuit 2 provides an output signal P₃ which is given to a stop value detecting circuit 5. In the absence of a shutter release signal (not shown) to the exposure calculating circuit 3, the signal P₁ is at the "H" level. At this time, the input/output selecting circuit 2 is receiving a pulse signal consisting of a frequency clock provided as stop value data from the flash unit 1 to a terminal Q₀ and providing this signal as its output signal P₃ to the stop value detecting circuit 5. When the signal P₁ goes to the "L" level in response to a shutter release signal and also the signal P₂ goes to the "L" level with the increase of the dose of light from the flash unit 1 detected by the TTL flash automatic light dose control circuit 4 beyond a predetermined level, the input/output selecting circuit 2 supplies to the flash unit 1, a light dose control signal represented by the signal P₂ from the TTL flash automatic light dose control circuit 4. The stop value detecting circuit 5 is controlled by a signal P₄, which is provided from the exposure calculating circuit 3 and can assume either "H" level or "L" level. The exposure calculating circuit 3 calculates pulses of the signal P₃ for each period T during which the signal P₄ is periodically at the "H" level. When a predetermined number of pulses is reached, the circuit 5 confirms this to be the continuously generated normal stop value data. At this time, the circuit 5 supplies a stop value data confirmation signal P₅ and a frequency signal P₆ which is stop value data received as the signal P₃ to the exposure calculating circuit 5. The exposure calculating circuit 3 effects exposure calculation according to the signals P₅ and P₆.

A detailed example of the construction of the input/output selecting circuit 2, flash unit 1 and stop value detecting circuit 5, these constituting the essential parts of the circuit of FIG. 1, will now be described with reference to FIGS. 2 and 3. Referring to FIG. 2, designated at E₁ is a power supply for the control of the flash unit 1. It also serves as a power supply for charging a flashlight bulb (not shown). A transistor Tr₁ has its collector connected to the plus side of the power supply E₁ and its emitter connected to through a load resistor R₁ to the minus side of the power supply. The base of the transistor Tr₁ constitutes an input terminal IN, to which stop value data consisting of a frequence clock is supplied. The data noted above is transmitted to a terminal Q₀ which is connected to the emitter of the transistor Tr₁. Au automatic light dose control signal based on the signal P₂ from the input/output selecting circuit 2, is supplied from the input/output selecting circuit 2 through an output terminal OUT, which is connected to the emitter of the transistor Tr₁, for controlling the stopping of the flashing of a flashing element (not shown) in the flash unit 1. A transistor Tr₁ has its collector connected to the plus side of a power supply E₂ for the control of camera and its base connected through a resistor R₂ to the plus side of the power supply E₂. The base is also connected through transistors Tr₃ and Tr₄ in parallel with each other to the minus side of the power supply E₂. The transistor Tr₂ is "on" when the transistors Tr₃ and Tr₄ are both "off" and is "off" when either one of the transistors Tr₃ and Tr₄ is "on". The transistor Tr₃ is turned on when the signal P₁ fed through the resistor R₃ goes to the "H" level. The transistor Tr₄ is turned on when the signal P₂ fed through the resistor R₄ goes to the "H" level. The emitter of the transistor Tr₂ is connected to the terminal Q₀ and is also connected through resistors R₅ and R₆ to the minus side of the power supply E₂. When the signal P₁ supplied to the transistor Tr₃ goes to the "L" level, the transistor Tr₃ is turned off. At this time, the signal P₂ received by the transistor Tr₄ either turns on or off the transistor Tr₄, thus inverting the signal P₂ sent out to the output terminal OUT. The transistor Tr₅ has its collector connected to a load resistor R₇ to the minus side of the power source E₂ and its emitter connected to the minus side of the power supply. The base of the transistor Tr₅ receives a potential, which is obtained by dividing the potential V_(Q0) at the terminal Q₀ between the resistors R₅ and R₆. The output signal P₃ is supplied from the collector of the transistor Tr₅ through the inverter G₁ to the stop value detecting circuit 5. The condition to be met for the signal P₃ to be at the "H" level is given as ##EQU1## where V_(BE) is the threshold value of the base potential for the transistor Tr₅ to be turned on so that "L" level is provided from the collector thereof. The resistances of the resistors R₅ and R₆ are determined such as to meet the inequality noted above; more particularly, these values are set such that the inequality be satisfied irrespective of the fluctuations of the potential V_(BE) due to changes in temperature of the transistor Tr₅ or irrespective of the fluctuations of the potential V_(Q0) due to fluctuations of the voltages of the power supplies E₁ and E₂. As for the signal P₃, a signal provided when and only when the transistor Tr₂ is "off", i.e., a signal provided according to the stop value data IN, is used, and the signal provided through the transistor Tr₂ on the bais of the light dose signal P₂ is not used, as will be described hereinafter in detail. Referring to FIG. 3, D-type flip-flops F₁, F₂ and F₃ constitute a counter. The signal P₄ from the exposure calculating circuit 3 is coupled through delay circuits G₂ and G₃ to the reset terminals R of flip-flops F₁, F₂ F₃. An output signal provided from an AND gate G₄ is fed to the gate terminal C₁ of the D-type flip-flop F₁. The negation output terminal Q₁ is connected to the gate terminal C₂ of the D-type flip-flop F₂, the negation output terminal Q₂ is in turn fed to the gate terminal C₃ of the D-type flip-flop F₃, and the negation output terminal Q₃ is connected to the other input terminal of the AND gate G₄. The AND gate G₄ receives at its input terminal noted before the output signal P₃ from the input/output selecting circuit 2. In each D-type flip-flop its negation output terminal Q and data input terminal D are connected to each other. The three flip-flops F₁, F₂ and F₃ which are connected in cascade are reset by the signal P₄. When four pulses are provided as the signal P₃ after the resetting of the flip-flops, the output from the affirmation output terminal Q of the last stage D-type flip-flop F₃ goes to the "H" level, this signal being fed to the data input terminal D₄ of a following stage D-type flip-flop F₄. The signal P₄ is supplied to the gate terminal C₄ of the D-type flip-flop F₄. When this signal P₄ goes to the "H" level, the output from the affirmation output terminal Q₄ goes to the "H" level due to the "H" level signal to the input terminal D₄ noted above. At this time, it is confirmed that the signal P₃ is the normal frequency signal. A confirmation signal P₅ which is produced at this time is supplied to the exposure calculating circuit 3 and also to an AND gate G₅. The AND gate G₅ thus passes the signal P₃ fed to its other input terminal as the frequency signal P₅ to the exposure calculating circuit 3. When the exposure calculating circuit 3 receives the release signal, it inverts the signal P₄ to the "L" level while blocking the signals P₅ and P₆.

The operation of the above construction will now be described.

In the light measuring operation, as soon as charging is completed, stop value data which consists of a frequency clock is supplied to the input terminal IN of the flash unit 1, i.e., the base of the transistor Tr₁. At this time, the signal P₁ of the exposure calculating circuit 3 is at the "H" level since no release signal is received. Thus, the transistor Tr₃ is "on", while the transistor Tr₂ is "off". The frequency clock as the stop value data noted above is thus transmitted to the terminal Q₀ with the action of the transistor Tr₁. The frequency clock operates the transistor Tr₅, and the signal P₃ is supplied to the AND gate G₃ after the instant t₀ of completion of charging as shown in FIG. 4. The exposure calculating circuit 3 is accepting the signals P₅ and P₆ while it is providing a timing pulse signal with a period T as shown in FIG. 4 to the stop value detecting circuit 5. If the signal P.sub. 4 is at the "L" level at the instant t₀, the D-type flip-flops F₁, F₂ and F₃ are in the reset state after having been set once. The negation output terminal Q₃ of the flip-flop F₃ is this at the "H" level. Thus, the signal P₃ is passed through the AND gate G₄ to the gate terminal C₁ of the flip-flop F₁. The flip-flops F₁, F₂ and F₃ which constitute a counter are repeating a counting operation such that with the second rising of the signal P₃ at the gate terminal C₁ a rising signal is fed to the gate terminal C₂ of the flip-flop F₂ and likewise with the second rising of the signal at the gate terminal C₂ a rising signal is fed to the gate terminal C₃ of the flip-flop F₃. When the signal P₄ goes to the "H" level at an instant t₁, the individual flip-flops F₁, F₂ and F₃ are reset, and when the resetting is subsequently released with the inversion of the signal P₄ to the "L" level, the flip-flops F₁, F₂ and F₃ start counting afresh. The counting in the individual state flip-flops proceeds with the second rising of the input to the gate terminal in the preceding stage flip-flops. With the fourth rising of the signal P₃, the output of the affirmation output terminal Q of the flip-flop F₃ is thus inverted to the "H" level. The "H" level signal is fed to the data input terminal D₄ of the D-type flip-flop F₄. As a result, the output of the negation output terminal Q₃ of the flip-flop F₃ is inverted to the "L" level, thus causing the AND gate G₄ to pass the signal P₃. When the signal P₄ goes to the "H" level at an instant t₂, the output of the affirmation output terminal Q₄ of the flip-flop F₄ goes to the "H" level. This signal supplied as the confirmation signal P₅ to the exposure calculating circuit 3. The signal P₄ is delayed a slight delay time through the delay circuits G₂ and G₃ before it is coupled to the flip-flops F₁, F₂ and F₃ for resetting these flip-flops at an instant t₃. Since the affirmation output terminal Q₄ of the flip-flops at an instant t₃. Since the affirmation output terminal Q₄ of the flip-flop F₄ is at the "H" level, the signal P₃ is subsequently passed through the AND gate G₅ to be fed as the frequency signal P₆ to the exposure calculating circuit 3. While the signal P₃ continues to prevail, the signals P₅ and P₆ are not changed. This is so because always four or more pulses are generated as the signal P₃ during a period T₀ shown in FIG. 4 so that the data input terminal D₄ of the flop-flop F₄ is always at the "H" level before the rising of the signal P₄. Since the confirmation signal P₅ is at the "H" level, the exposure calculating circuit 3 accepts the frequency signal P₆ as the normal signal.

With the appearance of a release signal not shown, the exposure operation of the camera is started. First, the exposure calculating circuit 3 executes calculations necessary for the exposure. At the same time, the circuit 3 renders the signal P₁ to be at the "L" level and also renders the signal P₄ to be at the "L" level while blocking the signals P₅ and P₆. When the camera shutter is subsequently fully opened, the flash unit 1 is caused to produce flashlight with the closure of a switch (not shown). At this time, the automatic light dose control signal P₂ is at the "H" level, that is, the transistor Tr₄ is "on" while the transistor Tr₂ is "off". When the TTL flash automatic light dose control circuit 4 detects a predetermined light dose level, the signal P₂ goes to the "L" level to turn off the transistor Tr₄. The transistor Tr₃ at this time remains "off" since the signal P₁ is at the "L" level. Thus, the transistor Tr₂ is turned on so that a flashing stop signal is provided to the output terminal OUT. The flash unit 1 stops flashing in response to the flashing stop signal. While the signal P₃ is generated with the action of the transistor Tr₂, this gives rise to no trouble in the operation of the camera for the signals P₅ and P₆ are blocked. These also arises a situation, in which the output of the transistor Tr₁ and the output of the transistor Tr₂ appear simultaneously at the terminal Q₀ during a period from the instant when the signal P₁ is inverted from the "H" level to the "L" level with the generation of the release signal till the flashing of the flash unit 1. This again gives rise to no trouble for the transistor Tr₂ is "on" at this time.

As has been described in the foregoing, according to the present invention stop value data is counted for a fixed period of time and the exposure calculating section is adapted to accept the count when and only when the count is confirmed to be the normal signal. Thus, there is no possibility of accepting noise, nor there is any possibility for the stop value data to be adversely affected by the fluctuations of the power supplies for the flash unit and camera. Further, since an input/output selecting circuit is provided, the stop value data and TTL automatic light dose control signal can be transmitted through a single terminal, so that it is possible to simplify the connection between the camera and flash unit. 

What is claimed is:
 1. In a camera which can be used with a flash unit connected to it for providing stop value data consisting of a frequency clock for controlling exposure according to said stop value data, a device for detecting stop value data from flash unit comprising a stop value detecting circuit for counting said frequency clock in a predetermined period of time and transmitting said frequency clock to an automatic stop control unit when the count reaches a predetermined value, and an input/output selecting circuit provided on the side of said stop value detecting circuit to which the stop value data from the flash unit is supplied and connected to a flash automatic light dose control circuit, said input/output selecting circuit transmitting said stop value data to said stop value detecting circuit when there is no shutter release signal while transmitting a light dose control signal from said flash automatic light dose control circuit to said flash unit when there is a shutter release signal. 